1. Field of the Invention
This invention relates generally to doctors of the type employed in paper making machines and the like, and is concerned in particular with an improved oscillating doctor blade holder.
2. Description of the Prior Art
In a known doctor, as disclosed in U.S. Pat. No. 2,300,908 (Broughton), an unduly complex roller arrangement is employed to reciprocally support and guide the blade holder. In particular, mutually spaced sets of at least three rollers are required to act in concert to counteract the reactionary thrust and rotational forces exerted on the doctor blade holder during a doctoring operation.
Such arrangements are difficult to maintain, often requiring disassembly of the blade holder when roller replacement becomes necessary. The three roller arrangement is also difficult to seal and thus prone to a build up of contaminants between the roller sets. This in turn requires frequent cleaning and attention by maintenance personnel.
An objective of the present invention is to overcome the disadvantages of known oscillating doctor holders by providing a much simpler yet highly effective support arrangement.
To this end, in accordance with the present invention, a blade holder component extends longitudinally across a moving surface to be doctored. A doctor blade is carried by the blade holder component. A support component is parallel to and supports the blade holder component. A first operating means rotatably urges the doctor blade in one direction into contact with the moving surface to be doctored, resulting in the doctor blade being acted upon by a reactionary thrust force in the plane of the doctor blade, and a reactionary rotational force opposite to the direction of rotational blade application.
Guide rails on parallel tracks are provided on one of either the blade holder or support components, and rotatable rollers are spaced along the length of the other of the blade holder or support components. Each roller is in rolling contact with a guide rail on a respective one but not the other of the tracks to thereby accommodate reciprocal movement of the blade holder component relative to the support component, and at least some of the rollers coact with their respective guide rails to resist both the reactionary thrust and rotational forces acting on the doctor blade.
A second operating means reciprocally moves the blade holder component relative to the support component.
In certain preferred embodiments, the rollers have either curved or angularly profiled rims in rolling contact and in mechanical interengagement with mating curved or angularly disposed surfaces on the guide rails. The curved or angularly disposed surfaces of the guide rails may define longitudinal grooves extending in the direction of reciprocal movement of the blade holder component, with the curved or angularly profiled rims of the rollers projecting into the longitudinal grooves. Alternatively, the curved or angularly profiled rims of the rollers may define circular grooves, with the curved or angularly disposed surfaces of the guide rails projecting into the circular grooves.
The rollers may advantageously be grouped in pairs mounted on and spaced at intervals along the length of either the blade holder component or the support component. The rotational axes of the roller pairs may be offset in the direction of the length of the component on which they are mounted.
The rollers are preferably axially shiftable on their respective support shafts to thereby accommodate any minor misalignment and/or subsequent gradual wear of components.
These and other features, advantages and objectives of the present invention will now be described in greater detail with reference to the accompanying drawings, wherein: